Method of creating variable electrical resistance and means for creating the same

ABSTRACT

A variable magnetic resistor comprising a layer of high permeability magnetic alloy formed into a helix with a layer of insulation material in between each convolution of the helix, and an electrical terminal secured to opposite ends of the layer of alloy. The method of creating variable resistance by passing a current of sufficient magnitude through said alloy material that the current passing through the alloy will be forced to the side edges thereof by the magnetic field around each convolution of the helix, whereby the resistance of the alloy will be increased as current moves away from a normal low-voltage path through the broad expanse of the entire cross-sectional area of the coil to a more confined path at the side edges of the coil.

United States Patent Inventor Herman R. Person Columbus, Nebr. Appl. No.817,965 Filed Apr. 21, 1969 Division of Ser. No. 593,998, Nav. 14, 1966,

Pat. No. 3,480,832. Patented May 25, 1971 Assignee Dale Electronics,Inc.

Columbus, Nebr.

METHOD OF CREATING VARIABLE ELECTRICAL RESISTANCE AND MEANS FOR CREATINGTHE SAME 3 Claims, 6 Drawing Figs.

U.S. Cl 0, 338/32, 338/282, 338/297, 338/223, 336/232 Int. Field ofSearch 338/20, 21, 32, 32 (H), 297, 279, 282; 336/223, 232

References Cited UNITED STATES PATENTS 2,821,685 1/1958 Whitehorn2.980,874 4/1961 Tarbox 336/192 2,998,583 8/1961 Worcester 336/232X3,016,507 1/1962 Grant et al... 338/32 3,172,032 3/1965 Hunt 338/32(H)3,286,161 11/1966 Jonesetal. 338/32X Primary Examiner-Richard A. FarleyAssistant Examiner-T. H. Tubbesing An0rneyZar1ey, Mc Kee and ThomteABSTRACT: A variable magnetic resistor comprising a layer of highpermeability magnetic alloy formed into a helix with a layer ofinsulation material in between each convolution of the helix, and anelectrical terminal secured to opposite ends of the layer of alloy. Themethod of creating variable resistance by passing a current ofsufficient magnitude through said alloy material that the currentpassing through the alloy will be forced to the side edges thereof bythe magnetic field around each convolution of the helix, whereby theresistance of the alloy will be increased as currentmoves away from anormal low-voltage path through the broad expanse of the entirecross-sectional area of the coil to a more confined path at the sideedges of the coil.

METHOD OF CREATING VARIABLE ELECTRICAL RESISTANCE AND MEANS FOR CREATINGTHE SAME This is a divisional application of my copending applicationSer. No.593,998 filed Nov. 14, 1966, now US. Pat. No. 3,480,832 datedNov. 25, 1969.

This invention relates to an electrical surge arrestor and in particularto a protector unit which will react quickly to protect a load in thecircuit from high surges of voltage from transient voltages such aslightning charges or the like.

A protector that uses a spark gap-type arrestor does not fire as rapidlyas desired when fast rising voltage transients are applied to the inputterminals of the arrestor and therefore the equipment attached to theoutput terminals of the circuit are frequently damaged by the spurts ofhigh voltage.

This invention involves a surge arrestor circuit having a spark gaparrestor connected across the input and being in parallel with abreakdown voltage regulator diode. The output of the surge arrestor isthen connected directly to the input with the two devices in parallelwith one another across the input and output. This circuit allows thediode to filter or clamp the voltages appearing on the output of thebreakdown voltage of the diode. This tends to filter out the spurt ofvoltage that would appear across the output due to the fact that thearrestor does not fire instantaneously. The breakdown of the mainelectrodes of the arrestor shorts out the transmission line and thevoltage across the output terminals is essentially reduced to zero, andas a consequence, protection of the equipment connected to the output isprovided.

This invention further involves the use of a pulse transformer where theprimary coil of the transformer is connected in series with the Zenerdiodes and thesecondary coil is connected to the third element of thesurge arrestor. The surge arrestors main electrodes will then beinitiated by the small breakdown occurring between the third element andone of the main electrodes caused by the pulse of voltage coming fromthe pulse transformer when the Zener diodes break down.

Preferred breakdown regulator diode used in the surge arrestor circuitis a Zener diode that has a characteristic of maintaining very smallcurrent flow through it until the breakdown or Zener voltage has beenreached, whereupon the diode starts conducting and continues to conductwhile the voltage across the diode remains substantially constant. Thissharp rising current through the pulse transformer causes a pulse ofvoltage to appear across the main electrode and the third electrode ofthe surge arrestor which causes breakdown, which in turn causes theionization of the main gap in the arrestor.

This invention further involves the use of a variable resistor forprotecting the breakdown voltage diode whereby upon the voltage acrossthe diode reaching the breakdown level a sharp rise in the currentthrough the variable resistor occurs which causes an increase in theresistance of the variable resistor. The variable resistor offers littleresistance to constant value currents but increases substantially inresistance as the rate of change of current increases. The increase inenergy then stored in the resistor is dissipated and thus protects thediode. Accordingly, the variable resistor which is preferably a mag:netic resistor permits DC current or low frequency AC current to flowthrough the arrestor without appreciable voltage drop, but yet allowshigh voltage drop to appear across the magnetic resistor during the timethe diode is passing current.

The variable magnetic resistor employed preferably involves a coil ofconductive permeable material having terminals at opposite ends of theconductive sheet material whereby upon the passage of currenttherethrough the phenomena of skin effect occurs which involves thecurrent being forced to the outer edges of the sheet material when thereis a high rate of change in the current level. The faster the change ofcurrent the faster the change of the magnetic field in the resistor andthus the greater the resistance to flow of current since the current isforced to the outer edges of the... sheet material. The operation of thevariable magnetic resistor is somewhat similar to an inductor exceptthat the resistor does not store the energy to be later applied to thecircuit but rather dissipates it within the resistor.

Another feature of this invention is to provide two pairs of diodesconnected in parallel with resistors in between the pairs of diodes andthe breakdown voltage of the first pair nearest the input and having theprimary coil of the pulse transformer therebetween being the highest andthe voltage across the second pair of diodes next to the output beingthe value desired for the output connected to the equipment. Any timethe voltage across the load and the second set of diodes reaches thebreakdown voltage of the second set of diodes, the diodes fire andthereby maintain the constant predetermined desired voltage. The firstset of diodes must fire first and consequently the resistors between thefirst and second set of diodes causes a voltage drop therebetweenassuring that a high voltage is applied across the first set of diodesrelative to the voltage across the second set of diodes.

Thus this invention consists in the construction, arrangements, andcombination of the various parts of the invention, whereby the purposescontemplated are attained as hereinafter more fully set forth,specifically pointed out in the claims, and illustrated in theaccompanying drawings, in which:

FIG. 1 is a schematic drawing of the electrical circuitry of theelectrical surge arrestor;

FIG. 2 is a plan view of the conductive permeable material of thevariable magnetic resistor;

FIG. 3 is a plan view of the insulative material employed in thevariable magnetic resistor;

FIG. 4 is an end view of the variable magnetic resistor in a looselycoiled condition;

FIG. 5 is an end view of the assembled magnetic variable resistor; and

FIG. 6 is a side elevation view of the magnetic variable resistor.

The electrical surge arrestor circuit includes a pair of input terminalsI0 and 12 with leads l4 and 16 connected to an-arrestor unit 18 having apair of primary terminals 20 and 22 in spaced apart relationship.

A pair of output terminals 24 and 26 are connected to a load 28. Theinput terminals 10 and 12 are connected to the output terminals 24 and26 by conductor lines 30 and 32.

Extending between the conductor lines 30 and 32 are a pair of Zenerdiodes 34 and 36 having their output sides connected to opposite sidesof a primary coil 38 included in a pulse transformer 40. The pulsetransformer 40 includes a secondary coil 42 having one lead connected toa third terminal 44 in spaced relationship to the primary terminals 20and 22 in the arrestor I unit 18. The other lead 46 of the secondarycoil is connected to the line 14.

A pair of magnetic variable resistors 48 and 50 are placed in the lines30 and 32 between the arrestor l8 and the Zener diodes 34 and 36.

A second pair of Zener diodes 52 and 54 interconnected in series areconnected across the conductor lines 30 and 32 in parallel relationshipto the first set of Zener diodes 34 and 36. A pair of resistors 56 and58 are positioned between the two sets of diodes to produce a voltagedrop from the first set to the second set.

The magnetic variable resistors 48 and 50 are shown in detail in FIGS.2, 3, 4, 5 and 6. They each include a sheet of conductive permeablematerial 60 having terminal pins 62 and 64 at opposite ends thereof asseen in FIG. 2. The material 60 should be a high permeability magneticalloy, such as soft iron. A sheet of insulative material 66 is shown inFIG. 3 and is coiled with the conductive material 60 as shown in FIG. 4.In FIGS. 5 and 6, the magnetic variable resistor 48 is shown in itscompleted form relatively tightly wound compared to the loosely woundunit in FIG. 4.

The variable magnetic resistors increase in resistance when thefrequency of the current through the resistors increase. This is knownas the skin effect and it is enhanced by the shape of the resistor andthe permeability of the resistor element. When low frequency AC currentor direct current is flowing through the resistor there is very littlemagnetic field produced and therefore the resistance of the resistor isvery low, However, as the frequency of the current changes the magneticfield increases thereby forcing the current passing through the resistorto the outer edges 68 and 70 (FIG. 2) where there is a relatively smallarea compared to the flat surface area of the conductive sheet material60 and consequently the resistance is substantially increased. Theresistor provides no inductive impedance but instead dissipatescompletely all energy that is stored in it as a result of a change inthe current frequency. it is apparent then that as the rate of change ofthe current increases the resistance value of the resistor will alsoincrease and accordingly the resistance of the resistor is a function ofthe current frequency.

It should be noted that the layers of material 60 and insulativematerial 62 are wound helically upon each other. The magnetic fields inone layer" of material 60 enhance the above-described skin effect inother layers. With normal DC current applied to the resistors, currentis Spread across the width of material 60. However, when the current isincreased, the magnetic buildup in the center of the material forces thecurrent to the edges to create the above-described skin effect, whichgreatly increases resistance.

The operation of the electrical surge arrestor circuit involves thefollowing sequence. The normal voltage for the load 28 is applied to theinput terminals and 12. The object of the surge arrestor circuit is toprotect the load 28 by maintaining a constant'voltage across theterminals 24 and 26 at the load 28. When a transient voltage such as acharge of lightning or the like appears across the input terminals 10and 12, the Zener diodes 34 and 36 will break down when this transientvoltage exceeds the breakdown voltage of these diodes. At the breakdownvoltage of the diodes a heavy current is drawn through the diodes andthe primary coil 38 of the pulse transformer 40 and the magneticresistors. The rise time of this current is relatively fast due to thesharp knee in the voltage characteristics of the Zener diodes. Thissharp rise in current through the' pulse transformer causes a pulse orvoltage to appear across the two electrodes 44 and 22 of the arrestor18. This voltage causes these two electrodes to break down therebyionizing the gap between the two terminals and 22 because the voltageacross the arrestor at this time is high enough to sustain the arebetween the two main electrodes 20 and 22. This breakdown of the mainelectrodes 20 and 22 essentially shorts out the transmission lines 30and 32 thus causing the voltage across the output terminals 24 and 26 tobe reduced to zero thereby providing the protection for the load unit 28that is desired.

The magnetic resistors 48 and 50 allow the DC current or low frequencyAC current to flow through the arrestor without appreciable voltagedrop, but yet allow a high voltage drop to appear across them during thetime the Zener diodes 34 and 36 are fired. The increase in energy thenstored in the variable resistors 48 and 50 is dissipated in theincreased resistance caused by the skin effect. And thereby the diodes34 and 36 are protected against damage from the transient voltageapplied to the input terminals 10 and 12. It is to be noted that aninductor if substituted for the variable resistors 48 and 50 would onlyhold the energy and later discharge it thereby causing the undesireddamage to the Zener diodes 34 and 36.

The Zener diodes 52 and 54 are connected across the output to insurethat the voltage on the output terminals never exceeds the rated voltagethat the load unit 28 connected to the output terminals 24 and 26 canwithstand. These are required because the voltages that will appearacross the first set of Zener diodes 34 and 36 will be slightly higherthan the breakdown voltages of the second set of Zener diodes S2 and 54because of the primary coil 38 of the pulse transformer 40 causing asmall voltage drop. This pulse that will appear across the first set ofZener diodes 34 and 36 will be of low magnitude and of short durationand will easily be dissi ated by the Zener diodes 52 and 54. The Zenerdio cs 52 an 54 must have a slightly lower breakdown voltage than theZener diodes 34 and 36, however, the Zener diodes 34 and 36 must breakdown first before the Zener diodes 52 and 54. Accordingly, it isnecessary to have the resistors 56 and 58 to insure this occurrence. Thesecond set of Zener diodes 52 and 54 would be selected on the basis ofhaving a breakdown voltage equal to the desired voltage across theoutput terminals 24 and 26 such that when the breakdown voltage isreached the voltage will not be increased due to the firing of thediodes and consequently maintaining the constant voltage across thediodes and the output terminals.

lclaim: 1. In a magnetic variable resistor, a first layer of a highpermeability magnetic material, a second layer of insulative material,said layers being relatively thin with respect to their length andwidth, and being wound upon each other in helical fashion so that oneend of said layers will appear at the substantial center of theresulting helix and the other ends of said layers will appear at theouter periphery of said resulting helix, and means on the ends of saidfirst layer for making electrical connections thereto whereby a voltageon said helix through said electrical connections in sufficient magnitude that the current passing through said helix will be forced to theside edges thereof by the magnetic field around each convolution of thehelix and the resistance of the helix will be increased as the currentmoves away from a normal low-voltage path through the broad expanse ofthe entire cross-sectional area of the helix to a more confined path atthe side edges of the helix.

2. The resistor of claim 1 wherein said first layer is comprised of softiron.

3. A method for creating variable electrical resistance in an electricalcircuit comprising,

coiling a thin elongated strip of high permeability magnetic alloyhaving two ends and two side edges into a helical coil with aninsulative material between each convolution of said coil,

connecting a terminal lead to one end of said strip at the center ofsaid coil and another terminal lead to the other end of said coil at theouter periphery of said coil;

connecting said terminal leads into an electrical circuit having anelectrical power source adapted to pass electrical current through saidcoil; and

varying the magnitude of current introduced to said coil by said powersource whereby said coil will increase in resistance at a rateproportional to the rate of variance of said current and will dissipatea substantial amount of the energy stored therein as a result of saidvariance of said current.

1. In a magnetic variable resistor, a first layer of a high permeabilitymagnetic material, a second layer of insulative material, said layersbeing relatively thin with respect to their length and width, and beingwound upon each other in helical fashion so that one end of said layerswill appear at the substantial center of the resulting helix and theother ends of said layers will appear at the outer periphery of saidresulting helix, and means on the ends of said first layer for makingelectrical connections thereto whereby a voltage on said helix throughsaid electrical connections in sufficient magnitude that the currentpassing through said helix will be forced to the side edges thereof bythe magnetic field around each convolution of the helix and theresistance of the helix will be increased as the current moves away froma normal low-voltage path through the broad expanse of the entirecross-sectional area of the helix to a more confined path at the sideedges of the helix.
 2. The resistor of claim 1 wherein said first layeris comprised of soft iron.
 3. A method for creating variable electricalresistance in an eLectrical circuit comprising, coiling a thin elongatedstrip of high permeability magnetic alloy having two ends and two sideedges into a helical coil with an insulative material between eachconvolution of said coil, connecting a terminal lead to one end of saidstrip at the center of said coil and another terminal lead to the otherend of said coil at the outer periphery of said coil; connecting saidterminal leads into an electrical circuit having an electrical powersource adapted to pass electrical current through said coil; and varyingthe magnitude of current introduced to said coil by said power sourcewhereby said coil will increase in resistance at a rate proportional tothe rate of variance of said current and will dissipate a substantialamount of the energy stored therein as a result of said variance of saidcurrent.